Only save cache if running on main (#7460)

.github/workflows/ci.yaml

@@ -48,7 +48,10 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy
-      - uses: Swatinem/rust-cache@v2
+
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          save-if: ${{ github.ref == 'refs/heads/main' }}
 
       - name: Install macOS dependencies
         uses: ./.github/actions/install-macos-deps
@@ -131,9 +134,10 @@ jobs:
         with:
           persist-credentials: false
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
         with:
           prefix-key: v0-rust-${{ join(matrix.targets, '-') }}
+          save-if: ${{ github.ref == 'refs/heads/main' }}
 
       - name: Install dependencies
         uses: ./.github/actions/install-linux-deps
@@ -280,7 +284,9 @@ jobs:
 
       - uses: dtolnay/rust-toolchain@stable
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          save-if: ${{ github.ref == 'refs/heads/main' }}
 
       - uses: actions/setup-python@v6.2.0
         with:
@@ -436,7 +442,9 @@ jobs:
           toolchain: ${{ env.NIGHTLY_CHANNEL }}
           components: miri
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          save-if: ${{ github.ref == 'refs/heads/main' }}
 
       - name: Run tests under miri
         run: cargo +${{ env.NIGHTLY_CHANNEL }} miri test -p rustpython-vm -- miri_test
@@ -457,7 +465,10 @@ jobs:
 
       - uses: dtolnay/rust-toolchain@stable
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+
       - name: install wasm-pack
         run: curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
       - name: install geckodriver
@@ -525,7 +536,10 @@ jobs:
         with:
           target: wasm32-wasip1
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+
       - name: Setup Wasmer
         uses: wasmerio/setup-wasmer@v3